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    SubjectRe: [PATCH] [RFT] crypto: aes-generic - turn off -ftree-pre and -ftree-sra
    On Wed, Jan 3, 2018 at 6:36 PM, Ard Biesheuvel
    <ard.biesheuvel@linaro.org> wrote:
    > On 3 January 2018 at 16:37, Arnd Bergmann <arnd@arndb.de> wrote:
    >> On Fri, Dec 22, 2017 at 4:47 PM, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
    >>
    >> A minimal patch would be to disable UBSAN specifically for aes-generic.c
    >> for gcc-7.2+ but not gcc-8 to avoid the potential stack overflow. We could
    >> also force building with -Os on gcc-7, and leave UBSAN enabled,
    >> this would improve performance some 3-5% on x86 with gcc-7 (both
    >> 7.1 and 7.2.1) and avoid the stack overflow.
    >>
    >
    > Can't we just disable UBSAN for that file for all GCC versions and be
    > done with it? It is not a production feature, and that code is
    > unlikely to change in ways where UBSAN would make a difference anyway,
    > nor is it ever executed on 99.9% of systems running Linux.

    It's up to Herbert in the end. I'm leaning to the -Os change in the Makefile,
    since it improves the performance for the common case as well, and
    once we start disabling UBSAN for performance-critical files, it becomes
    a slippery slope.

    I'll send the patch with the -Os change as v2, and note the ubsan-disabling
    alternative in the changelog.

    Arnd

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